The present invention is generally directed to methods of making flexible polyurethane foams from a mixture of one or more polyols and a catalyst that comprises cesium fluoride or rubidium fluoride, where the mixture is reacted with at least one isocyanate. Optionally, amine or ammonium containing catalysts and metal catalysts may also be present in the foam forming mixture. Preferably, the foaming reaction is performed in the absence of metallic catalysts, and in the absence of amines or ammonium-containing compounds (gelling and blowing catalysts).
Flexible cellular polyurethane structures typically are prepared by generating a gas during polymerization of a liquid reaction mixture comprised of a polyester or polyether polyol, an isocyanate, a surfactant, catalyst and one or more blowing agents. The gas causes foaming of the reaction mixture to form the cellular structure. The surfactant stabilizes the structure.
Polyurethane foams with varying density and hardness may be formed. Tensile strength, tear strength, compression set, air permeability, flame retardancy, thermal conductivity, fatigue resistance, support factor, and cell size distribution may also be varied, as can many other properties. Specific foam characteristics depend upon the selection of the starting materials, the foaming process and conditions, and sometimes on the subsequent processing.
Catalysts are used to control the relative rates of water-isocyanate (gas-forming) and polyol-isocyanate (gelling) reactions. The catalyst may be a single component, or in most cases a mixture of two or more compounds. Heretofore, preferred catalysts for polyurethane foam production were organotin salts and tertiary amines. The amine catalysts are known to have a greater effect on the water-isocyanate reaction, whereas the organotin catalysts are known to have a greater effect on the polyol-isocyanate reaction. Total catalyst levels generally vary from 0 to 5.0 parts by weight per 100 parts polyol. The amount of catalyst used depends upon the formulation employed and the type of catalyst selected. Control of the gelling catalyst level is critical to producing foams with desired air permeability, which is a factor known to significantly affect foam cushioning performance. However, metallic catalysts, such as organotin catalysts, are toxic to health. Thus, one objective is to produce flexible polyurethane foams with desired air permeability and other foam properties without using metallic catalysts, or at least limiting the amount of metallic catalysts in the foaming mixture. And, gelling and blowing catalysts have been known to produce polyurethane foams with significant levels of volatile organic compound (VOC) emissions. Another objective is to produce flexible polyurethane foams with acceptable rise times, yet having reduced VOC emissions.
Therefore, improvements to flexible polyurethane foam production continue to be sought.